Sound control apparatus



Au8.20, 1940 c. M. CHORPENING 2,212,389

SOUND CONTROL APPARATUS Filed Sept. 29. 1938 CREED M.CH0RPEN1NG I 20eral amplitude of the lower frequencies.

.Patented Aug. 20, 1940 PATENT OFFICE 2,212,389 SOUND CONTROL APPARATUSCreed M. Chorpening, Youngstown, Ohio, assignor to Astatic MicrophoneLaboratory, Inc., Youngstown, Ohio, a corporation of Ohio ApplicationSeptember 29, 1938, Serial No. 232,357

4 Claims.

'Ihis invention relates to a sound reproducing system, and moreparticularly to a method and apparatus for controlling sound reproducedfrom a record. The invention is especially applicable 5 to a system inwhich a condenser type generator, as a piezo-electric crystal, isutilized as the pick-up element and has as its principal object theprovision of a pick-up circuit which will simultaneously compensate forlow frequency I0 deficiency in the amplitude of the recording andprovide `frequency' discriminating characteristics whereby the soundreproduced will be of high fidelity and controlled tone. "For reasonswell understood in the art it is common practice to record the lowerfrequencies (below approximately 250 cycles per second) at constant waveamplitude and the higher frequencies at constant needle velocity whichresults in substantial curtailment of the volume or gen- Inasmuch as atranslating device of the kind mentioned,'if sufiicient load resistanceis provided,

has an output proportional to the Wave amplitude or'`amplitudeof'vibration regardless of yfrequency,'its normal output is constant forthe lower frequencies and declines steadily asv the higher frequencies"'are reached.' `rNow by providing means discriminating against the lowerfrequencies the output of `the'pick-up may be rendered substantiallyconstant throughout the audio frequency range thus providing a responseof high fidelity.

In the reproduction of sound and particularly in reproduction of soundfrom records a certain amount of objectional noise resulting fromextraneous pick-up of signals composed principally of the higherfrequencies is reproduced and unless some means against such frequenciesthe final reproduction may be unsatisfactory. Also it is desirable toutilize such means to compensatefor variations in the characteristics ofthe pick-up device, for

desired low or high frequency preponderance in the sound being pickedup, forl imperfections in the frequency response of the loudspeaker, and

for other purposes well understood in the art.

Accordingly, a further object of the invention is the provision of apickup circuit requiring but simply constructed and inexpensiveelectrical accessories by means of which the tonal qualities of thesound being reproduced may be satisfactorily controlled simply byactuating a three position switch of conventional design and connectedinto the signal circuit between the pickup and the amplier.

is provided to discriminatel The invention will be ydescribed by way ofex ample with reference to a reproducing system, shown schematically inthe drawing in which the pickup device hereinbefore mentionedis atranslator of the piezo-electric crystal type,y the 5 invention beingparticularly adaptable to such use. Other objects and advantages of the`invention should become apparent asthe description proceeds.

In the drawing: c 1o'v Figure l is a schematic diagram of a systemembodying'my invention for reproducing'sound from phonograph records;and

Figure 2 is a graph illustrating the character y istics of operation ofthe tone controlofmy in- 15 vention.

Referring now to Figure 1, the piezo-electric translator, generallyindicated at I0, is physically actuated by the stylus II and isvconnected p through circuit I2-I6 and conductor 25.,to a 20 suitableamplifier 28 which in turn feeds loud-l speaker 32 through conductors30. The circuit referred to consists ofvconductor I2, a fixed resistanceI3, conductor I4, a variable resistance I5. constituting the volumecontrol, ,and con- -25 ductor I6. A condenser I9 has one of its ter-`minals connected with an arm 20 of athreepoint switch I1, the centerterminal 22 of which is open. The other two terminals of the switch 2|and 23 are connected, respectively, with con- 30 ductors I2 and 25leading from the translator device l0.

With the switch arm 20 in the neutral position shown in the drawing,condenser I 9 is ineffectual and the impedance of the pickup circuit issolely 35 that of the fixed resistance I3 and the variable resistance I5in series in the circuit. This condition results in a volume-frequencyrelation graphically shown by curve C22 in Figure 2. With switch arm 20moved to contact terminal 40 2l, theA capacitance of I9 is placed inseries with the pickup circuit and in parallel with resistance I3resulting in relative attenuation of the lower frequency signals andemphasizing the higher frequency responses. The result of the series 45coupling of the condenser I9 is depicted graphically by thevolume-frequency curve C2I of Figure 2.

'I'he third terminal 23 of switch I1 being connected with the conductor23 places condenser 50 I9 in shunt relation with translator I0 whenswitch arm 20 is moved to contact this terminal and in this condition ofthe circuit the higher frequency responses are more severelydiscriminated against resulting in a volume-frequency 55 relationindicated by curve C23 of Figure 2. It has been found that the abovedescribed three circuit conditions provide an adequate control of thesound reproduction under all methods and conditions of detection andthat for all ordinary purposes a finer degree of control is unnecessary,It should be observed that the control is accomplished simply by themanipulation of a conventional three point switch which is readilyinstalled and operated and which is not likely to fail in service.

In practice, I have found that a resistance ofy approximately 1 megohmis suitable for resistance I3 and that 1/2 megohm resistance is suitablefor resistance l5. The capacity of condenser I9 may, of course, bevaried depending onA the characteristic of the translator but in generalit may be in the nature of .0005 microfarad when coupled with acommercial double piezo-electric crystal actuated by a stylus as shown.

It can thus be seen that I-have provided a tone control for use asdescribed which accomplishes the objectives initially set out. By theuse of a simple arrangement the signal response from the translator iscaused to selectively flow either through a circuit having only seriesresistance in which the various frequencies maintain their normalrelative strength, through a circuit having series coupled capacitancein which the lower fre- SiQlquencies are attenuated, or through acircuit having shunted capacitance in which the higher frequencies areattenuated. The arrangement is further simplified by utilizing the samemeans, specifically the condenser I9, to providethe ca- 3Q; pacitance inboth instances.

4Q? ing, the broken line represents the Volume Yor amplitude of therecording and shows the decrease in the lower frequency range. The lineC22 represents the response attained when sufficient resistance isplaced in the output circuit 45j to render the output proportional tothe amplitude of` vibration of the pickup stylus. The respense is -iiatat lower frequencies and curves downwardly in the4 higher ranges. Bycoupling the condenser i9 across resistance I3 the higherl frequencysignals are relatively strengthened, giving a response curve illustratedby line C2| and resulting in high fidelity production.

The above specifically described embodiment ci' my invention should beconsidered as illustrative only as obviously many variations in thearrangement of the frequency discrimination method specificallydisclosed herein may be made without departing from the spirit or scopeof my invention. l

What I claim is:

l. In a sound reproducing system, a source of audio frequency signalscomprising a piezo-electric translating element,a circuit connectingsaid element with a sound reproducing assembly, frequency discriminatingmeans comprising two impedance elements connected with said circuit, theilrst impedance element being a resistance fixed in rseries relationwith said circuit, the second irnpedance element being a condenser,means to conne-ct said condenser in series relation with said circuitand shunting said resistance, means to connect said vcondenser inparallel with said resistance and translator, and means to disconnectsaid condenser from said circuit.

- 2. A system according to claim 1 in which said lastthree mentionedmeans comprise a unitary three position switch.

3. In a. sound reproducing system, a source of audio frequency signals,a circuit connecting said source with a sound reproducing assembly,vfrequency discriminating means comprising tWo impedance elementsconnected with said circuit, the rst impedance element being aresistance fixed in series relation with said circuit, the secondimpedancey element being a condenser, means to connect said condenser inseries relation with said circuit andv shunting said resistance, meansto connect said condenser in parallel with said resistance andtranslator, and means togdisconnect said condenser from said circuit.

4. A system according to claim 3 in which said last three mentionedmeans comprise a unitary three position switch.

f A CREED M. CHORPENING.

